tailieunhanh - Corrosion Control Through Organic Coatings P05

Các chuyên ngành cơ bản của cơ khí bao gồm: động học, tĩnh học, sức bền vật liệu, truyền nhiệt, động lực dòng chảy, cơ học vật rắn, điều khiển học, khí động học, thủy lực, chuyển động học và các ứng dụng nhiệt động lực học. Các kỹ sư cơ khí cũng đòi hỏi phải có kiến thức và năng lực áp dụng những khái niệm trong môi trường kỹ thuật điện và hóa học. Với một mức độ nhỏ, cơ khí còn trở thành kỹ thuật phân tử - một mục tiêu viễn cảnh của nó là tạo. | 5 Abrasive Blasting and Heavy-Metal Contamination In the previous chapter mention was made of the need to minimize spent abrasive when blasting old coatings containing lead pigments. This chapter covers some commonly used techniques to detect lead chromium and cadmium in spent abrasive and methods for disposing of abrasive contaminated with lead-based paint LBP chip or dust. Lead receives the most attention both in this chapter and in the technical literature. This is not surprising because the amount of lead in coatings still in service dwarfs that of cadmium barium or chromium. The growing body of literature on the treatment of lead-contaminated abrasive seldom distinguishes between the various forms of lead found in old coatings although toxicology literature is careful to do so. Red lead Pb3O4 for example is the most common lead pigment in old primers and white lead PbCO3 Pb OH 2 is more commonly found in old topcoats. It is unknown whether or not these two lead pigments will leach out at the same rate once they are in landfills. It is also unknown whether they will respond to stabilization or immobilization treatments in a similar manner. A great deal of research remains to be done in this area. DETECTING CONTAMINATION There are really two questions involved in detecting the presence of lead or other heavy metals 1. Does the old paint being removed contain heavy metals 2. Will the lead leach out from a landfill The amount of a metal present in paint is not necessarily the amount that will leach out when the contaminated blasting media and paint has been placed in a landfill 1-3 . The rate at which a toxic metal leaches out depends on many factors. At first leaching comes from the surface of the paint particles. The initial rate therefore depends most on the particle size of the pulverized paint. This in turn depends on the condition of the paint to be removed the type of abrasive used and the blasting process used 4 . Eventually as the polymeric backbone .